Method for reporting in wireless communication system and device supporting same

ABSTRACT

Provided is a method for reporting carried out by a terminal in a wireless communication system. The method comprises: receiving a public land mobile network (PLMN) list, which is information on one or more of PLMNs on which a logged minimization drive test (MDT) is valid; receiving information for executing the logged MDT; logging a measurement on the basis of the information for executing the logged MDT; entering a target cell in a radio resource control (RRC) connected state; determining whether or not the logged measurement is reportable; and if determined possible to report to the target cell, reporting the whole or a part of the logged measurement to the target cell. Whether or not the logged measurement can be reported is determined on the basis of the PLMN list.

TECHNICAL FIELD

The present invention relates to a wireless communication system, andmore particularly, to a Minimization Drive Test (MDT) measurement andradio link failure report method and an apparatus supporting the same ina wireless communication system under a multiple Public Land MobileNetwork (PLMN) environment.

BACKGROUND ART

3^(rd) Generation Partnership Project (3GPP) Long Term Evolution (LTE),that is, the improvement of an LTE Universal Mobile TelecommunicationsSystem (UMTS), has been introduced as 3GPP release 8. 3GPP LTE usesOrthogonal Frequency Division Multiple Access (OFDMA) in downlink anduses Single Carrier-Frequency Division Multiple Access (SC-FDMA) inuplink. 3GPP LTE adopts Multiple Input Multiple Output (MIMO) having amaximum of 4 antennas. Recently, 3GPP LTE-Advanced (LTE-A), that is, theevolution of 3GPP LTE, is being discussed.

A Minimization Drive Test (MDT) is that service providers perform a testusing UE instead of a vehicle for coverage optimization. Coverage variesdepending on the location of a BS, the deployment of peripheralbuildings, and a user use environment. Accordingly, a service providerneeds to periodically perform a driving test, and lots of costs andresources are consumed. An MDT is that a service provider measurescoverage using UE.

An MDT can be divided into a logged MDT and an immediate MDT. Inaccordance with the logged MDT, UE performs MDT measurement and thentransfers logged measurement to a network at a specific point of time.In accordance with the immediate MDT, UE performs MDT measurement andthen transfers measurement to a network when a report condition issatisfied. In the logged MDT, MDT measurement is performed in an RRCidle mode, whereas in the immediate MDT, MDT measurement is performed inan RRC connected mode.

A service provider can write a coverage map, indicating whether or notservice is possible over the entire area to which service is provided bya service provider and a distribution of QoS, by synthesizing pieces ofMDT measurement received from several pieces of UE and use the writtencoverage map in network operations and optimization. For example, when areport on a coverage problem for a specific area is received from UE, aservice provider can enlarge the coverage of a corresponding area cellby increasing the transmission power of a BS that provides service tothe corresponding area.

If one service provider manages a plurality of Public Land MobileNetworks (PLMNs) or a plurality of service providers manages a pluralityof PLMNs in a wireless communication system, existing MDT measurement ora radio link failure report can be limited. This is because theexecution of the MDT measurement or the radio link failure report can belimited to a cell corresponding to the Registered PLMN (RPLMN) of UE.

In the limited MDT measurement and/or radio link failure report in awireless communication system under such a multiple PLMN environment,there may occur a problem in that the effectiveness of a measured orsensed report on a generated event is reduced because information aboutthe measured or sensed report cannot be continuously reported to anetwork. Accordingly, there is a need for a method for guaranteeing thecontinuity of a measurement report according to MDT measurement and/or areport on information about a radio link failure in wirelesscommunication under a multiple PLMN environment.

DISCLOSURE Technical Problem

An object of the present invention is to provide a Minimization DriveTest (MDT) measurement and/or radio link failure report method and anapparatus supporting the same, which can guarantee continuity in amultiple PLMN environment.

Technical Solution

In an aspect, a method for reporting performed by user equipment (UE) ina wireless communication system is provided. The method includesreceiving a Public Land Mobile Network (PLMN) list that is informationabout at least one PLMN whose logged Minimization Drive Test (MDT) isvalid, receiving information for executing the logged MDT, loggingmeasurement based on the information for executing the logged MDT,entering a Radio Resource Control (RRC)_connected state for a targetcell, determining whether reporting the logged measurement is possibleor not; and reporting part of or full logged measurement to the targetcell if reporting the logged measurement to the target cell is possible.The step of determining that whether reporting the logged measurement ispossible or not is based on the PLMN list.

The PLMN list may include at least one identity of the at least onePLMN.

The step of determining whether reporting the logged measurement ispossible or not may include determining that reporting the loggedmeasurement to the target cell is possible, if an identity of a PLMN forthe target cell is included in the at least one identity of the at leastone PLMN in the PLMN list and the logged measurement to be reported tothe target cell is present.

The PLMN list and the information for performing the logged MDT may betransmitted in a logged measurement configuration that is an RRCmessage.

The step of reporting the part of or the full logged measurement to thetarget cell comprises sending a logged measurement-available indicatorto the target cell, the logged measurement-available indicatorindicating that the logged measurement to be reported to the target cellis present, receiving a measurement report request from the target cellas a response to the logged measurement-available indicator, and sendingthe part of or the full logged measurement to the target cell inresponse to the measurement report request.

The information for the logged MDT measurement may include loggingduration indicating duration for which the logged MDT is performed, anda logging interval indicating an interval in which the logging isperformed.

The step of logging the measurement may include logging measurementevery interval within the logging duration from a point of time at whichthe information for the logged MDT measurement is received, andsuspending the logging when the duration elapses.

In another aspect, a wireless apparatus is provided. The wirelessapparatus includes a transceiver transmitting and receiving radiosignals, and a processor is operably coupled to the transceiver. Theprocessor is configured to receive information for executing the loggedMinimization Driving Test (MDT), log measurement based on theinformation for executing the logged MDT, enter a Radio Resource Control(RRC)_connected state for a target cell, determine whether reporting thelogged measurement is possible or not, and report part of or full loggedmeasurement to the target cell if reporting the logged measurement tothe target cell is possible. The step of determining that whetherreporting the logged measurement is possible or not is based on the PLMNlist.

The PLMN list may include at least one identity of the at least onePLMN.

The step of determining whether reporting the logged measurement ispossible or not may include determining that reporting the loggedmeasurement to the target cell is possible, if an identity of a PLMN forthe target cell is included in the at least one identity of the at leastone PLMN in the PLMN list and the logged measurement to be reported tothe target cell is present.

The PLMN list and the information for performing the logged MDT may betransmitted in a logged measurement configuration that is an RRCmessage.

In still another aspect, a method for reporting performed by a userequipment (UE) in a wireless communication system is provided. Themethod includes receiving a Public Land Mobile Network (PLMN) list thatis information about a PLMN whose radio link failure report is valid,detecting a radio link failure, generating radio link failureinformation that is information about the radio link failure, entering aRadio Resource Control (RRC)_connected state for a target cell,determining whether reporting the radio link failure information to thetarget cell is possible or not, and reporting the radio link failureinformation to the target cell if reporting the radio link failureinformation to the target cell is possible. The step of determining thatwhether reporting the radio link failure information to the target cellis possible or not is based on the PLMN list.

The PLMN list may include at least one identity of the at least onePLMN.

The step of determining whether reporting the radio link failureinformation is possible or not may include determining that reportingthe radio link failure information to the target cell is possible if anidentity of a PLMN for the target cell is included in the at least oneidentity of the at least one PLMN in the PLMN list and the radio linkfailure information to be reported to the target cell is present.

Advantageous Effects

In accordance with a Minimization Drive Test (MDT) measurement methodaccording to the present invention, UE can determine whether or not toperform logging and a measurement report based on a PLMN scope. UE canreport logging and measurement for a permitted specific PLMN as well asfor a registered PLMN (RPLMN).

In accordance with a radio link failure report method according to thepresent invention, UE can determine whether or not to report informationabout a sensed radio link failure based on a PLMN scope. UE can reportinformation about a radio link failure for a permitted specific PLMN aswell as for an RPLMN.

A network can support MDT measurement in a cell corresponding to a PLMNin addition to an RPLMN and also support a radio link failure.Accordingly, network optimization can be embodied more efficientlybecause a (logged) measurement report and radio link failure informationhaving more guaranteed continuity are obtained.

DESCRIPTION OF DRAWINGS

FIG. 1 shows a wireless communication system to which the presentinvention is applied.

FIG. 2 is a block diagram showing a radio protocol architecture for auser plane.

FIG. 3 is a block diagram showing a radio protocol architecture for acontrol plane.

FIG. 4 is a flowchart illustrating the operation of UE in the RRC_idlestate.

FIG. 5 is a flowchart illustrating a process of setting up an RRCconnection.

FIG. 6 is a flowchart illustrating a process of reconfiguring an RRCconnection.

FIG. 7 is an exemplary diagram showing a radio link failure.

FIG. 8 is a flowchart illustrating the success of a connectionreestablishment process.

FIG. 9 is a flowchart illustrating the failure of a connectionreestablishment process.

FIG. 10 is a flowchart illustrating an existing method of performingmeasurement.

FIG. 11 shows an example in which a measurement identity is deleted.

FIG. 12 shows an example in which a measurement object is deleted.

FIG. 13 is a flowchart illustrating an existing measurement procedure.

FIG. 14 is a flowchart illustrating a method of performing a logged MDT.

FIG. 15 is a diagram showing an example of logged MDT measurementaccording to a logging area.

FIG. 16 is a diagram showing an example of logged MDT measurementaccording to a change of RAT.

FIG. 17 is a diagram showing an example of logged measurement.

FIG. 18 is a diagram showing an example of an immediate MDT.

FIG. 19 is a flowchart illustrating an example of a method of performinglogged MDT measurement based on a PLMN scope in accordance with anembodiment of the present invention.

FIG. 20 is a flowchart illustrating another example of a method ofperforming logged MDT measurement based on a PLMN scope in accordancewith an embodiment of the present invention.

FIG. 21 is a flowchart illustrating yet another example of a method ofperforming logged MDT measurement based on a PLMN scope in accordancewith an embodiment of the present invention.

FIG. 22 is a diagram showing an example of a method of reporting a radiolink failure based on a PLMN scope.

FIG. 23 is a block diagram showing a radio apparatus in which anembodiment of the present invention may be embodied.

MODE FOR INVENTION

FIG. 1 shows a wireless communication system to which the presentinvention is applied. The wireless communication system may also becalled an Evolved-UMTS Terrestrial Radio Access Network (E-UTRAN) or aLong Term Evolution (LTE)/LTE-A system.

The E-UTRAN includes a Base Station (BS) 20 which provides UserEquipment (UE) 10 with a control plane and a user plane. The UE 10 maybe fixed or may have mobility. The UE 10 may be called another term,such as a Mobile Station (MS), a User Terminal (UT), a SubscriberStation (SS), a Mobile Terminal (MT), or a wireless device. The BS 20refers to a fixed station communicating with the UE 10 and may be calledanother term, such as an evolved-NodeB (eNB), a Base Transceiver System(BTS), or an access point.

The BSs 20 may be interconnected through an X2 interface. The BS 20 isconnected to an Evolved Packet Core (EPC) 30 through an S1 interface,more particularly, to a Mobility Management Entity (MME) through anS1-MME and a Serving Gateway (S-GW) through an S1-U.

The EPC 30 includes the MME, the S-GW, and a Packet Data Network-Gateway(P-GW). The MME has access information about UE or information about thecapabilities of UE. Such information is chiefly used in the mobilitymanagement of UE. The S-GW is a gateway having an E-UTRAN as an endpoint, and the P-GW is a gateway having a PDN as an end point.

The layers of a radio interface protocol between UE and a network may beclassified into L1 (first layer), L2 (second layer), and L3 (thirdlayer) based on lower 3 layers of an Open System Interconnection (OSI)reference model which is widely known in communication systems. Fromamong the layers, the PHY layer belonging to the first layer providesinformation transfer service using physical channels, and a RadioResource Control (RRC) layer placed in the third layer functions tocontrol radio resources between UE and a network. To this end, the RRClayer exchanges RRC messages between UE and a BS.

FIG. 2 is a block diagram showing a radio protocol architecture for auser plane. FIG. 3 is a block diagram showing a radio protocolarchitecture for a control plane. A data plane is a protocol stack foruser data transmission, and a control plane is a protocol stack forcontrol signal transmission.

Referring to FIGS. 2 and 3, a physical (PHY) layer provides a higherlayer with information transfer service using physical channels. The PHYlayer is connected to a Medium Access Control (MAC) layer, that is, ahigher layer, through a transport channel. Data is moved between the MAClayer and the PHY layer through the transport channel. The transportchannel is classified depending on how data is transmitted through aradio interface according to what characteristics.

Data is transferred between different PHY layers, that is, between thePHY layers of a transmitter and a receiver, through a physical channel.The physical channel may be modulated according to an OrthogonalFrequency Division Multiplexing (OFDM) scheme, and the physical channeluses the time and frequency as radio resources.

The functions of the MAC layer include mapping between a logical channeland a transport channel and multiplexing/de-multiplexing to a transportblock that is provided to a physical channel on the transport channel ofan MAC Service Data Unit (SDU) that belongs to a logical channel. TheMAC layer provides service to a Radio Link Control (RLC) layer through alogical channel.

The functions of the RLC layer include the concatenation, segmentation,and reassembly of an RLC SDU. In order to guarantee various types ofQuality of Service (QoS) required by a Radio Bearer (RB), the RLC layerprovides three operation modes: a Transparent Mode (TM), anUnacknowledged Mode (UM), and an Acknowledged Mode (AM). AM RLC provideserror correction through an Automatic Repeat Request (ARQ).

The functions of a Packet Data Convergence Protocol (PDCP) layer in theuser plane include the transfer, header compression, and ciphering ofuser data. The functions of the PDCP layer in the user plane include thetransfer and ciphering/integrity protection of control plane data.

The Radio Resource Control (RRC) layer is defined only in the controlplane. The RRC layer is related to the configuration, re-configuration,and release of RBs and responsible for control of logical channels,transport channels, and physical channels. An RB means a logical paththat is provided by the first layer (PHY layer) and the second layers(the MAC layer, the RLC layer, and the PDCP layer) for the transfer ofdata between UE and a network.

What an RB is configured means a process of regulating thecharacteristics of a radio protocol layer and channel and configuringeach detailed parameter and operation method in order to providespecific service. An RB may be divided into a Signaling RB (SRB) and aData RB (DRB). The SRB is used as a passage along which an RRC messageis transported in the control plane, and the DRB is used as a passagealong which user data is transported in the user plane.

If an RRC connection is established between the RRC layer of UE and theRRC layer of an E-UTRAN, the UE is in an RRC connected state. If not,the UE is in the RRC_idle state.

A downlink transport channel through which data is transmitted from anetwork to UE includes a broadcast channel (BCH) through which systeminformation is transmitted and a downlink shared channel (SCH) throughwhich user traffic or control messages are transmitted. Traffic or acontrol message for downlink multicast or broadcast service may betransmitted through a downlink SCH or may be transmitted through anadditional downlink multicast channel (MCH). Meanwhile, an uplinktransport channel through which data is transmitted from UE to a networkincludes a random access channel (RACH) through which an initial controlmessage is transmitted and an uplink shared channel (SCH) through whichuser traffic or a control message is transmitted.

Logical channels placed over a transport channel and mapped to thetransport channel include a broadcast control channel (BCCH), a pagingcontrol channel (PCCH), a common control channel (CCCH), a multicastcontrol channel (MCCH), a multicast traffic channel (MTCH), and so on.

A physical channel includes several OFDM symbols in a time domain andseveral subcarriers in a frequency domain. One subframe consists of aplurality of OFDM symbols in the time domain. A resource block is aresource allocation unit, and a resource block consists of a pluralityof OFDM symbols and a plurality of subcarriers. Furthermore, eachsubframe may use specific subcarriers of specific OFDM symbols (e.g.,the first OFDM symbol) of a corresponding subframe for a physicaldownlink control channel (PDCCH), that is, an L1/L2 control channel. ATransmission Time Interval (TTI) is a unit time for subframetransmission.

An RRC state and RRC connection method of UE are described below.

An RRC state means whether or not the RRC layer of UE has been logicallyconnected with the RRC layer of an E-UTRAN. If the RRC layer of UE islogically connection with the RRC layer of an E-UTRAN, it is called theRRC_connected state. If the RRC layer of UE is not logically connectionwith the RRC layer of an E-UTRAN, it is called the RRC_idle state. SinceUE in the RRC_connected state has an RRC connection, an E-UTRAN maycheck the presence of the UE in a cell unit, and thus the UE may beeffectively controlled. In contrast, an E-UTRAN cannot check UE in theRRC_idle state, and UE in the RRC_idle state is managed by a CoreNetwork (CN) in a tracking area, that is, an area unit greater than acell. That is, the presence of UE in the RRC_idle state is checked in alarger area unit, and the UE in the RRC_idle state needs to move to theRRC_connected state in order to receive common mobile communicationservice, such as voice or data.

When a user first powers on UE, the UE first searches for a suitablecell and remains in the RRC_idle state in a corresponding cell. UE inthe RRC_idle state establishes an RRC connection with an E-UTRAN throughan RRC connection procedure when it needs to establish the RRCconnection and shifts to the RRC_connected state. A case where the UE inthe RRC_idle state needs to establish the RRC connection includesseveral cases. For example, the UE in the RRC_idle state establishes anRRC connection when it needs to send uplink data for a reason, such as acall attempt by a user, or when it sends a message in response to apaging message received from an E-UTRAN.

A Non-Access Stratum (NAS) layer placed over the RRC layer performsfunctions, such as session management and mobility management.

In order to manage the mobility of UE in the NAS layer, two states: EPSMobility Management-REGISTERED (EMM-REGISTERED) and EMM-DEREGISTERED aredefined. The two states are applied to UE and an MME. Initial UE is inthe EMM-DEREGISTERED state. In order for the UE to access a network, theUE performs a process of being registered with the network through aninitial attach procedure. If the attach procedure is successfullyperformed, the UE and the MME become the EMM-REGISTERED state.

In order to manage signaling connection between UE and an EPC, twostates: an EPS Connection Management (ECM)-IDLE state and anECM-CONNECTED state are defined. The two states are applied to UE and anMME. If UE in the ECM-IDLE state establishes an RRC connection with anE-UTRAN, the UE becomes the ECM-CONNECTED state. If an MME in theECM-IDLE state establishes an S1 connection with the E-UTRAN, the MMEbecomes the ECM-CONNECTED state. When UE is in the ECM-IDLE state, anE-UTRAN does not have context information about the UE. Accordingly, theUE in the ECM-IDLE state performs a mobility-based procedure based UE,such as cell selection or cell reselection, without a need to receive acommand from a network. In contrast, when UE is in the ECM-CONNECTEDstate, the mobility of the UE is managed by a command from a network. Ifthe location of UE is different from a location known to a network inthe ECM-IDLE state, the UE informs the network of the location of the UEthrough a tracking area update procedure.

System information is described below.

System information includes essential information that needs to be knownby UE in order to access a BS. Accordingly, the UE needs to havereceived all pieces of system information before accessing the BS andneeds to always have recent system information. Furthermore, systeminformation is information that needs to be known by all pieces of UEwithin one cell, and thus a BS periodically transmits the systeminformation.

In accordance with Paragraph 5.2.2 of 3GPP TS 36.331 V8.7.0 (2009-09)“Radio Resource Control (RRC); Protocol specification (Release 8)”,system information is classified into a Master Information Block (MIB),a Scheduling Block (SB), and a System Information Block (SIB). The MIBenables UE to know the physical configuration of a corresponding cell,for example, a bandwidth. The SB informs information about thetransmission of SIBs, for example, a transport period. The SIB is acollection of pieces of correlated system information. For example, anySIB includes only information about neighboring cells, and any SIBincludes only information about an uplink radio channel used by UE.

In general, service provided from a network to UE may be classified intothree types as follows. Furthermore, UE differently recognizes the typeof cell depending on what service may be received. A service type isfirst described, and the type of cell is then described.

1) Limited service: this service provides an emergency call and anEarthquake and Tsunami Warning System (ETWS), and this service can beprovided by an acceptable cell.

2) Normal service: this service means public use for common purposes,and this service can be provided by a suitable or normal cell.

3) Operator service: this service means service for a communicationnetwork service provider, and this cell can be used only by acommunication network service provider, but cannot be used by a commonuser.

In relation to a service type provided by a cell, the type of cell canbe classified as follows.

1) Acceptable cell: a cell from which UE can be provided with limitedservice. This cell is a cell which is not barred from a viewpoint ofcorresponding UE, but satisfies a cell selection criterion for the UE.

2) Suitable cell: a cell from which UE can be provided with suitableservice. This cell satisfies a condition for an acceptable cell and alsosatisfies an additional condition. The additional condition includesthat this cell needs to belong to a Public Land Mobile Network (PLMN)accessible to corresponding UE and this cell must be a cell on which atracking area update procedure is not barred from being executed by UE.If a corresponding cell is a CSG cell, the CSG cell needs to be a cellthat UE can access as a CSG member.

3) Barred cell: a cell that broadcasts that this cell is a cell barredthrough system information.

4) Reserved cell: a cell that broadcasts that this cell is a cellreserved through system information.

FIG. 4 is a flowchart illustrating the operation of UE in the RRC_idlestate. FIG. 4 shows a procedure in which UE that is initially powered onis registered with a network through a cell selection process and the UEperforms cell reselection, if necessary.

Referring to FIG. 4, the UE selects Radio Access Technology (RAT) forcommunicating with a Public Land Mobile Network (PLMN), that is, anetwork from which the UE is provided with service (S410). Informationabout the PLMN and the RAT may be selected by the user of the UE, andinformation stored in a Universal Subscriber Identity Module (USIM) maybe used.

The UE selects a cell having the greatest value from cells whosemeasured BS and signal intensity or quality is greater than a specificvalue (S420). In this case, powered-on UE performs cell selection, whichmay be called initial cell selection. Cell selection procedure isdescribed in detail later. After the cell selection, the UE receivessystem information that is periodically transmitted by a BS. Thespecific value refers to a value defined in a system in order toguarantee quality for a physical signal in data transmission/reception.Accordingly, the value may be different depending on applied RAT.

If the UE needs to be registered with a network, the UE performs anetwork registration procedure (S430). The UE registers its owninformation (e.g., IMSI) with the network in order to receive service(e.g., paging) from the network. The UE does not register itsinformation with an accessing network whenever the UE selects a cell,but registers its information with a network if information (e.g.,Tracking Area Identity (TAI)) about the network received from systeminformation is different from information about the network which hasbeen known to the UE.

The UE performs cell reselection based on a service environment providedby a cell, the environment of the UE, etc. (S440). If a value of theintensity or quality of a signal measured from a BS that providesservice to the UE is lower than a value measured from a BS of aneighboring cell, the UE selects a cell from other cells that providebetter signal characteristics than the cell of the BS that the UE hasaccessed. This process is called cell reselection differently from theinitial cell selection of second process. Here, in order to prevent acell from being frequently reselected depending on a change of signalcharacteristics, a temporal restriction condition is imposed. The cellreselection procedure is described in detail later.

FIG. 5 is a flowchart illustrating a process of setting up an RRCconnection.

UE transmits an RRC connection request message, requesting an RRCconnection, to a network (S510). The network transmits an RRC connectionsetup message in response to the RRC connection request (S520). Afterreceiving the RRC connection setup message, the UE enters an RRCconnected mode.

The UE transmits an RRC connection setup complete message, used to checkthe successful completion of the RRC connection setup, to the network(S530).

FIG. 6 is a flowchart illustrating a process of reconfiguring an RRCconnection. An RRC connection reconfiguration is used to modify an RRCconnection. This is used to set up, modify/release an RB, performhandover, and set up, modify/release measurement.

A network transmits an RRC connection reconfiguration message formodifying an RRC connection to UE (S610). The UE transmits an RRCconnection reconfiguration complete message used to check the successfulcompletion of an RRC connection reconfiguration to the network inresponse to the RRC connection reconfiguration (S620).

A radio link failure is described below.

UE continues to perform measurement in order to maintain the quality ofa radio link to a serving cell from which service is received. The UEdetermines whether or not communication is impossible in a currentsituation due to the deterioration of quality of a radio link to aserving cell. If communication is almost impossible because the qualityof a serving cell is too low, the UE determines a current situation tobe a radio connection failure.

If a radio link failure is determined, the UE forgives maintainingcommunication with a current serving cell, selects a new cell through acell selection (or cell reselection) procedure, and attempts an RRCconnection reestablishment to the new cell.

FIG. 7 is an exemplary diagram showing a radio link failure. Anoperation related to a radio link failure may be described in twophases.

In the first phase, UE performs a normal operation and checks whether ornot there is a problem in a current communication link. If a problem isdetected, the UE declares a radio link problem and waits for therecovery of a radio link for a first standby time T1. If the radio linkis recovered before the first standby time elapses, the UE performs anormal operation again. If the radio link is not recovered until thefirst standby time expires, the UE declares a radio link failure andenters the second phase.

In the second phase, the UE waits for the recovery of the radio link fora second standby time T2. If the radio link is not recovered until thesecond standby time expires, the UE enters the RRC_idle state. Or, theUE may perform an RRC reestablishment procedure.

The RRC connection reestablishment procedure is a procedure ofreestablishing an RRC connection again in the RRC_connected state. Sincethe UE remains in the RRC_connected state, that is, since the UE doesnot enter the RRC_idle state, the UE does not initialize all its radioconfigurations (e.g., radio bearer configurations). Instead, the UEsuspends the use of all radio bearers other than an SRB0 when startingan RRC connection reconfiguration procedure. If an RRC connectionreconfiguration is successful, the UE resumes the use of suspended radiobearers.

FIG. 8 is a flowchart illustrating the success of a connectionreestablishment process.

UE selects a cell by performing cell selection. The UE receives systeminformation in order to receive basic parameters for cell access in theselected cell. Furthermore, the UE sends an RRC connectionreestablishment request message to a BS (S810).

If the selected cell is a cell having the context of the UE, that is, aprepared cell, the BS accepts the RRC connection reestablishment requestof the UE and transmits an RRC connection reestablishment message to theUE (S820). The UE transmits an RRC connection reestablishment completemessage to the BS, so the RRC connection reestablishment procedure canbe successful (S830).

FIG. 9 is a flowchart illustrating the failure of a connectionreestablishment process. UE transmits an RRC connection reestablishmentrequest message to a BS (S810). If a selected cell is not a preparedcell, the BS transmits an RRC connection reestablishment reject messageto the UE in response to the RRC connection reestablishment request(S815).

A procedure of UE selecting a cell is described in detail below.

When UE is powered on or the UE remains in a cell, the UE performsprocedures for receiving service by selecting/reselecting a cell havingsuitable quality.

UE in the RRC_idle state always needs to select a cell having suitablequality and to be prepared to receive service through this cell. Forexample, UE that is just powered on needs to select a cell havingsuitable quality in order to be registered with a network. When the UEin the RRC_connected state enters the RRC_idle state, the UE needs toselect a cell in which the UE will remain in the RRC_idle state. Aprocess in which the UE selects a cell that satisfies any condition inorder to remain in a service standby state, such as the RRC_idle state,as described above is called cell selection. An important point is thatthe UE needs to select a cell as rapidly as possible because cellselection is performed in the state in which the UE has not determined acell in which the UE will remain in the RRC_idle state. Accordingly, ifa cell provides the quality of a radio signal higher than a certainreference, although the cell is not a cell that provides the bestquality of a radio signal to the UE, the cell may be selected in thecell selection process of the UE.

A method and procedure of UE selecting a cell in 3GPP LTE are describedbelow with reference to 3GPP TS 36.304 V8.5.0 (2009-03) “User Equipment(UE) procedures in idle mode (Release 8)”.

When UE is initially powered on, the UE searches for an available PublicLand Mobile Network (PLMN) and selects a suitable PLMN from whichservice may be received. The PLMN is a network that is deployed ormanaged by a mobile network operator. Each mobile network operatormanages one or more PLMNs. Each PLMN can be identified by Mobile CountryCode (MCC) and Mobile Network Code (MNC). Information about the PLMN ofa cell is included in system information and broadcasted. UE attempts toregister a selected PLMN. If the registration is successful, theselected PLMN becomes a Registered PLMN (RPLMN). A network may signal aPLMN list to the UE. PLMNs included in the PLMN list may be consideredto be the same PLMNs as RPLMNs. UE registered with a network needs to bealways reachable by the network. If UE is in the ECM-CONNECTED state(identically an RRC_connected state), a network recognizes that the UEis provided with service. If the UE is in the ECM-IDLE state(identically the RRC_idle state), the situation of the UE is not validin an eNB, but is stored in an MME. In this case, only the MME isinformed of the location of the UE in the ECM-IDLE state as thegranularity of a list of Tracking Areas (TAs). A single TA is identifiedby a Tracking Area Identity (TAI) including a PLMN identity to which theTA belongs and Tracking Area Code (TAC) that uniquely represent a TAwithin a PLMN.

Next, the UE selects a cell having signal quality and characteristicsfrom which the UE can be provided with suitable service from cellsprovided by the selected PLMN.

A cell selection process is chiefly divided into two types.

First, as an initial cell selection process, in this process, UE doesnot have preliminary information about a radio channel. Accordingly, inorder to find a suitable cell, the UE searches all radio channels. TheUE searches each channel for the strongest cell. Next, the UE selects acorresponding cell only if it has only to find a suitable cell thatsatisfies a cell selection reference.

Next, the UE may select a cell using stored information or usinginformation broadcasted by a cell. Accordingly, cell selection may befaster than an initial cell selection process. The UE selects acorresponding cell if it has only to find a cell that satisfies a cellselection reference. If a suitable cell that satisfies the cellselection reference is not found through this process, the UE performsan initial cell selection process.

After UE selects any cell through a cell selection process, theintensity or quality of a signal between the UE and a BS may be changeddue to the mobility of the UE or a change of a radio environment.Accordingly, if the quality of a selected cell is deteriorated, the UEmay select another cell that provides better quality. If a cell isselected again as described above, the UE selects a cell that providesbetter signal quality than a currently selected cell. This process iscalled cell reselection. In general, the cell reselection process has abasic object to select a cell that provides the best quality to UE froma viewpoint of the quality of a radio signal.

In addition to the viewpoint of the quality of a radio signal, a networkcan determine priority by the frequency and inform UE of the determinedpriority. The UE which has received the priority preferentiallyconsiders this priority to be higher than a radio signal qualityreference in a cell reselection process.

There is a method of selecting or reselecting a cell based on the signalcharacteristics of a radio environment as described above. Upon cellreselection, in selecting a cell for reselection, the following cellreselection method may be used depending on the RAT and frequencycharacteristics of a cell.

-   -   Intra-frequency cell reselection: A reselected cell is a cell        having the same center-frequency and the same RAT as those used        in a cell on which the UE is currently being camped.    -   Inter-frequency cell reselection: A reselected cell is a cell        having the same RAT and a different center-frequency with        respect to those used in the cell on which the UE is currently        being camped.    -   Inter-RAT cell reselection: A reselected cell is a cell using a        different RAT from a RAT used in the cell on which the UE is        currently being camped.

The principle of a cell reselection process is as follows.

First, UE measures the quality of a serving cell and a neighboring cellfor cell reselection.

Second, cell reselection is performed based on a cell reselectionreference. The cell reselection reference has the followingcharacteristics in relation to the measurement of the serving cell andthe neighboring cell.

Intra-frequency cell reselection is basically based on ranking. Rankingis a task for defining a criterion value for cell reselection evaluationand ranking cells using the criterion value in order of a highercriterion value. A cell having the best criterion is commonly called thebest ranked cell. The cell criterion value is a value to which afrequency offset or a cell offset has been applied, if necessary, on thebasis of a value measured by UE for a corresponding cell.

Inter-frequency cell reselection is based on frequency priority providedby a network. UE attempts to camp on a frequency having the highestfrequency priority. A network may provide frequency priority that willbe in common applied by pieces of UEs within a cell through broadcastsignaling or may provide frequency-dedicated priority according to eachpiece of UE through UE-dedicated signaling.

For inter-frequency cell reselection, a network may provide UE with aparameter (e.g., a frequency-specific offset) used in cell reselectionby the frequency.

For intra-frequency cell reselection or inter-frequency cellreselection, a network may provide UE with a Neighboring Cell List (NCL)used in cell reselection. The NCL includes a cell-specific parameter(e.g., a cell-specific offset) used in cell reselection.

For intra-frequency or inter-frequency cell reselection, a network mayprovide UE with a cell reselection black list used in cell reselection.UE does not perform cell reselection on a cell that is included in theblack list

Ranking performed in a cell reselection evaluation process is describedbelow.

A ranking criterion used to assign priority to a cell is defined as inEquation 1.

R _(s) =Q _(meas,s) +Q _(hyst) ,R _(n) =Q _(meas,n) +Q_(offset)  [Equation 1]

Here, R_(s) is a ranking criterion for a serving cell, R_(n) is aranking criterion for a neighboring cell, Q_(meas,s) is a quality valuemeasured by UE in relation to a serving cell, Q_(meas,n) is a qualityvalue measured by UE in relation to a neighboring cell, Q_(hyst) is ahysteresis value for ranking, and Q_(offset) is an offset between twocells.

In Intra-frequency, if UE receives an offset Q_(offsets,n) between aserving cell and a neighboring cell, Q_(offset)=Q_(offsets,n). If UEdoes not receive Q_(offsets,n), Q_(offset)=0.

In Inter-frequency, if UE receives an offset Q_(offsets,n) for acorresponding cell, Q_(offset)=Q_(offsets,n)+Q_(frequency). If UE doesnot receive Q_(offsets,n), Q_(offset)=Q_(frequency).

If the ranking criterion R_(s) of a serving cell and the rankingcriterion R_(n) of a neighboring cell are shifted in a similar state, UEmay alternately reselect two cells because ranking priority isfrequently changed as a result of the shift. Q_(hyst) is a parameterthat prevents UE from alternately reselecting two cells by giving ahysteresis in cell reselection.

UE measures R_(s) of a serving cell and R_(n) of a neighboring cellaccording to the above equation, considers a cell having the greatestranking criterion value to be the best ranked cell, and reselects thecell.

In accordance with the reference, it may be seen that the quality of acell functions as the most important reference in cell reselection. If areselected cell is not a suitable cell, UE excludes a correspondingfrequency or a corresponding cell from the subject of cell reselection.

Measurement and a measurement report are described below.

In a mobile communication system, the mobility support of UE isessential. Accordingly, UE consistently measures quality for a servingcell which now provides service and quality for a neighboring cell. UEreports a measurement result to a network on a suitable time, and anetwork provides the UE with the optimal mobility through handover, etc.Measurement for this purpose is called Radio Resource Management (RRM)Measurement.

In addition to the mobility support object, in order to provideinformation that may help a service provider to manage a network, UE mayperform measurement for a specific object set by the network and reporta measurement result thereof to the network. For example, UE may receivebroadcast information about a specific cell that has been determined bya network. UE may report a cell identity of the specific cell (this isalso called a global cell identity), location identity information(e.g., tracking area code) to which the specific cell belongs and/orother cell information (e.g., whether or not the specific cell is amember of a Closed Subscriber Group (CSG) cell) to a serving cell.

If UE in motion checks that the quality of a specific area is very poorthrough measurement, the UE may report location information and ameasurement result of cells having poor quality to a network. Thenetwork may attempt to optimize the network based on a report onmeasurement results from pieces of UE that help the operation of thenetwork.

In a mobile communication system whose frequency reuse factor is 1,mobility is chiefly performed between different cells in the samefrequency band. Accordingly, in order to well guarantee the mobility ofUE, the UE needs to be able to well measure the quality of neighboringcells having the same center frequency as a serving cell and informationabout the cells. As described above, measurement for a cell having thesame center frequency as a serving cell is called intra-frequencymeasurement. UE performs intra-frequency measurement and reports ameasurement result to a network on a suitable time so that the object ofa corresponding measurement result is achieved.

A mobile communication service provider may manage a network using aplurality of frequency bands. If a communication system provides servicethrough a plurality of frequency bands, in order to guarantee optimalmobility for UE, the UE needs to be able to well measure the quality ofneighboring cells having a different center frequency from a servingcell and information about the cells. As described above, measurementfor a cell having a different center frequency from a serving cell iscalled inter-frequency measurement. UE needs to be able to performinter-frequency measurement and report a measurement result to a networkon a suitable time.

If UE supports measurement for a heterogeneous network, measurement maybe performed on a cell of a heterogeneous network based on a BSconfiguration. Such measurement for a heterogeneous network is calledinter-Radio Access Technology (RAT) measurement. For example, RAT mayinclude a UMTS Terrestrial Radio Access Network (UTRAN) and a GSM EDGERadio Access Network (GERAN) that comply with the 3GPP standard and mayalso include a CDMA 2000 system that complies with the 3GPP2 standard.

FIG. 10 is a flowchart illustrating an existing method of performingmeasurement.

UE receives measurement configuration information from a BS (S1010). Amessage including the measurement configuration information is called ameasurement configuration message. The UE performs measurement based onthe measurement configuration information (S1020). The UE reports ameasurement result to the BS if the measurement result satisfies areport condition within the measurement configuration information(S1030). A message including the measurement result is called ameasurement report message.

The measurement configuration information may include the followinginformation.

(1) Measurement object information: information about the object onwhich measurement will be performed by UE. The measurement objectincludes at least one of an intra-frequency measurement object that isthe object of intra-cell measurement, an inter-frequency measurementobject that is the object of inter-cell measurement, and an inter-RATmeasurement object that is the object of inter-RAT measurement. Forexample, the intra-frequency measurement object may indicate aneighboring cell having the same frequency band as a serving cell, theinter-frequency measurement object may indicate a neighboring cellhaving a different frequency band from a serving cell, and the inter-RATmeasurement object may indicate a neighboring cell having different RATfrom a serving cell.

(2) Reporting configuration information: information about a reportcondition regarding when UE reports a measurement result and about areport type. The report condition may include information about an eventor period in which a report on a measurement result is triggered. Thereport type is information regarding that a measurement result will beconfigured according to what type.

(3) Measurement identity information: information about a measurementidentity, which makes UE determine to report what measurement objectaccording to what type when in association with a measurement object anda reporting configuration. The measurement identity information isincluded in a measurement report message, and it may indicate that ameasurement result is about what measurement object and that ameasurement report has been generated under what report condition.

(4) Quantity configuration information: information about a parameterfor configuring the filtering a measurement unit, a report unit and/or ameasurement result value.

(5) Measurement gap information: information about a measurement gap,that is, an interval which may be used by UE for only measurementwithout taking data transmission to a serving cell into consideration,because DL transmission or UL transmission has not been scheduled.

In order to perform a measurement procedure, UE has a measurement objectlist, a measurement report configuration list, and a measurementidentity list.

In 3GPP LTE, a BS may configure only one measurement object for onefrequency band regarding UE. In accordance with Paragraph 5.5.4 of 3GPPTS 36.331 V8.5.0 (2009-03) “Evolved Universal Terrestrial Radio Access(E-UTRA) Radio Resource Control (RRC); Protocol specification (Release8)”, events triggered by a measurement report, such as those in thefollowing table, are defined.

TABLE 1 Events Report Conditions Event A1 Serving becomes better thanthreshold Event A2 Serving becomes worse than threshold Event A3Neighbour becomes offset better than serving Event A4 Neighbour becomesbetter than serving Event A5 Serving becomes worse than threshold1 andneigbour becomes better than threshold2 Event B1 Inter RAT neighborbecomes better than threshold Event B2 Serving becomes worse thanthreshold1 and inter RAT neighbor becomes better than threshold2

If the measurement report of UE satisfies a set event, the UE transmitsa measurement report message to a BS.

FIG. 11 shows an example of a measurement configuration configured forUE.

First, a measurement identity 1(1101) connects an intra-frequencymeasurement object and a reporting configuration 1. UE performsintra-frequency measurement, and the reporting configuration 1 is usedto determine a reference and report type for a measurement resultreport.

Like the measurement identity 1(1101), a measurement identity 2(1102) isconnected to the intra-frequency measurement object, but the measurementidentity 2(1102) connects the intra-frequency measurement object and areporting configuration 2. UE performs intra-frequency measurement, andthe reporting configuration 2 is used to determine a reference and areport type for a measurement result report.

Based on the measurement identity 1(1101) and the measurement identity2(1102), UE transmits a measurement result of the intra-frequencymeasurement object if the measurement result satisfies any one of thereporting configuration 1 and the reporting configuration 2.

A measurement identity 3(1103) connects an inter-frequency measurementobject 1 and a reporting configuration 3. UE reports a measurementresult of the inter-frequency measurement object 1 if the measurementresult satisfies a report condition included in the reportingconfiguration 1.

A measurement identity 4(1104) connects an inter-frequency measurementobject 2 and the reporting configuration 2. UE reports a measurementresult of the inter-frequency measurement object 2 if the measurementresult satisfies a report condition included in the reportingconfiguration 2.

Meanwhile, a measurement object, a reporting configuration and/or ameasurement identity may be added, changed and/or deleted. This may beindicated when a BS transmits a new measurement configuration message toUE or transmits a measurement configuration change message to the UE.

FIG. 12 shows an example in which a measurement identity is deleted.When a measurement identity 2(1102) is deleted, measurement for ameasurement object associated with the measurement identity 2(1102) issuspended, and a measurement report is not also transmitted. Ameasurement object or a reporting configuration associated with thedeleted measurement identity may not be changed.

FIG. 13 shows an example in which a measurement object is deleted. Whenan inter-frequency measurement object 1 is deleted, UE also deletes anassociated measurement identity 3(1103). Measurement for theinter-frequency measurement object 1 is suspended, and a measurementreport is also not transmitted. However, a reporting configurationassociated with the deleted intra-frequency measurement object 1 may notbe changed or deleted.

When a reporting configuration is removed, UE also removes an associatedmeasurement identity. UE suspends measurement for a measurement objectassociated by the associated measurement identity. However, ameasurement object associated with the deleted reporting configurationmay not be changed or deleted.

A measurement report may include a measurement identity, the measuredquality of a serving cell, and a measurement result of a neighboringcell. The measurement identity identifies a measurement object whosemeasurement report has been triggered. The measurement result of theneighboring cell may include a cell identity and measured quality of theneighboring cell. The measured quality may include at least one ofReference Signal Received Power (RSRP) and Reference Signal ReceivedQuality (RSRQ).

A Minimization Drive Test (MDT) is described below.

An MDT enables UE to perform measurement and report a result thereofinstead of a drive test in which conventional service providers measurethe quality of cells using vehicles for cell coverage optimization.Coverage varies depending on the location of a BS, the deployment ofperipheral buildings, and a use environment of a user. Accordingly, aservice provider needs to periodically perform a drive test, whichconsumes lots of costs and resources. In order to overcome thedisadvantages, there is proposed an MDT in which a service providermeasures coverage using UE.

A service provider may write a coverage map, indicating whether or notservice is possible over the entire area to which service is provided bya service provider and a distribution of QoS, by synthesizing MDTmeasurement values received from several pieces of UE and use thewritten coverage map in network operations and optimization. Forexample, when a report on a coverage problem for a specific area isreceived from UE, a service provider may enlarge the coverage of acorresponding area cell by increasing the transmission power of a BSthat provides service to the corresponding area. The time and costnecessary for network optimization can be minimized through such amethod.

An MDT has been produced based on the framework of a tracking function,that is, one of the tools of an operator for Operation, Administration,and Maintenance (OAM). The tracking function provides an operator withthe ability to perform tracking and to log the behaviors of UE and thuscan enable the operator to determine the major cause of a functionfailure on the UE side. Traced data is collected over a network, whichis called a Trace Collection Entity (TCE). An operator uses datacollected in a TCE for analysis and evaluation. A tracking function usedfor an MDT includes signaling based on a tracking function andmanagement based on tracking function. Signaling based on a trackingfunction is used to activate an MDT task toward specific UE, whereasmanagement based on tracking functions is used to activate an MDT taskwithout being limited to specific UE.

An MDT may be divided into two types: a logged MDT and an immediate MDTdepending on whether UE reports measured and stored log data in anon-real time or in real time. The logged MDT is a method of UEperforming MDT measurement, logging corresponding data, and sending thelogged data to a network. In contrast, the immediate MDT is a method ofUE performing MDT measurement and immediately sending corresponding datato a network. In accordance with the logged MDT, UE performs MDTmeasurement in the RRC_idle state. In accordance with the immediate MDT,UE performs MDT measurement in the RRC_connected state.

FIG. 14 is a flowchart illustrating a method of performing a logged MDT.

Referring to FIG. 14, UE receives a logged measurement configuration(S1410). The logged measurement configuration may be included in an RRCmessage and transmitted through a downlink control channel. The loggedmeasurement configuration may include at least one of a TCE ID,information about a reference time that is a basis for logging, loggingduration, a logging interval, and information about an areaconfiguration. The logging interval indicates an interval in which ameasurement result is stored. The logging duration indicates durationfor which UE performs a logged MDT. The reference time indicates areference time for duration for which a logged MDT is performed. Thearea configuration indicates an area that has been requested to belogged by UE.

Meanwhile, UE initiates a validity timer when a logged measurementconfiguration is received. The validity timer means the lifetime of thelogged measurement configuration, which may be specified by informationabout logging duration. The duration of the validity timer may indicatethe validity of measurement results owned by UE as well as the validlifetime of a logged measurement configuration.

A procedure in which UE performs a logged measurement configuration anda corresponding overall procedure is performed as described above iscalled a configuration phase.

When the UE enters the RRC_idle state (S1421), the UE logs themeasurement result while the validity timer is driven (S1422). Ameasurement result value may include RSRP, RSRQ, Received Signal CodePower (RSCP), Ec/No, etc. Information on which a measurement result hasbeen logged is called logged measurement. A temporal interval in whichUE logs a measurement result one or more times is called a loggingphase.

The execution of a logged MDT based on a logged measurementconfiguration by UE may vary depending on the location of the UE.

FIG. 15 is a diagram showing an example of a logged MDT according to alogging area.

A network may configure a logging area that is an area in which UE hasto log. The logging area may be represented as a cell list or a trackingarea/location area list. If a logging area is configured in UE, the UEsuspends logging when the UE gets out of the logging area.

Referring to FIG. 15, a first area 1510 and a third area 1530 are areasconfigured as logging areas, and a second area 1520 is an area in whichlogging is not permitted. UE performs logging in the first area 1510,but does not perform logging in the second area 1520. UE performslogging again when the UE moves from the second area 1520 to the thirdarea 1530.

FIG. 16 is a diagram showing an example of a logged MDT according to achange of RAT.

UE performs logging only when the UE camps on RAT from which a loggedmeasurement configuration has been received and suspends logging inanother RAT. However, the UE may log cell information about other RATsin addition to camp-on RAT.

A first area 1610 and a third area 1630 are E-UTRAN areas, and a secondarea 1620 is a UTRAN area. A logged measurement configuration isreceived from the E-UTRAN. When UE enters the second area 1620, the UEdoes not perform MDT measurement.

Referring back to FIG. 14, the UE enters the RRC_connected state(S1431). If logged measurement to be reported is present, the UE informsan eNB that the logged measurement to be reported is present (S1432).The UE may inform the eNB that the logged measurement is present when anRRC connection is established, an RRC connection is reestablished, or anRRC connection is reconfigured. Furthermore, if the UE performshandover, the UE may inform a handover target cell of a presence of thelogged measurement. Informing, by the UE, the eNB that the loggedmeasurement is present may include including a loggedmeasurement-available indicator, that is, indication informationinforming that the logged measurement is present, in an RRC messagetransmitted from the UE to the eNB and sending the RRC message. The RRCmessage may be an RRC connection configuration complete message, an RRCconnection reestablishment complete message, an RRC reconfigurationcomplete message, or a handover complete message.

When the eNB receives a signal informing that the logged measurement ispresent from the UE, the eNB request the UE to report logged measurement(S1433). Requesting the report on the logged measurement may includeincluding a logged measurement report request parameter regardinginformation indicative of the request in an RRC message and sending theRRC message. The RRC message may be a UE information request message.

When the UE receives the request to report the logged measurement fromthe eNB, the UE reports the logged measurement to the eNB (S1434).Reporting the logged measurement to the eNB may include including thelogged measurement report, including pieces of logged measurement, in anRRC message and sending the RRC message to the eNB. The RRC message maybe a UE information report message. In reporting the logged measurement,the UE may report all or some of pieces of logged measurement owned bythe UE on a report time point to the eNB. If the UE reports some ofpieces of logged measurement, the reported pieces of logged measurementmay be discarded.

A phase of a process in which the UE informs the eNB that the loggedmeasurement is present, receives a request to report the loggedmeasurement from the eNB, and reports the logged measurement isperformed as described above is called a report phase.

A radio environment is chiefly measured by the UE while a logged MDT isperformed. MDT measurement may include a cell identity and the signalquality and/or signal intensity of the cell. MDT measurement may includea measurement time and a measurement place. The following tableillustrates contents logged by UE.

TABLE 2 Parameter (set) Contents Serving Global cell identity of aserving cell cell identity Measurement result Measured RSRP of servingcell of serving cell Measured RSRQ of serving cell Measurement resultCell identities of measured E-UTRA cells, of neighbor cell Measurementresults of UTRA cells Cell identities of measured UTRA cells,Measurement results of UTRA cells Cell identities of measured GERANcells, Measurement results of GERAN cells Cell identities of measuredCDMA2000 cells, Measurement results of CDMA200 cells Time stamp Time oflogging measurement result, calculated (current time-reference time),calculated in seconds Location Detailed location information of loggingtime point information

Information logged at different logging time points can be classifiedand stored according to different log entries.

FIG. 17 is a diagram showing an example of logged measurement.

Logged measurement includes one or more log entries.

The log entry includes a logging location, a logging time, a servingcell identity, a serving cell measurement result, and a neighboring cellmeasurement result.

The logging location indicates the location where UE has performedmeasurement. The logging time indicates the time when UE has performedmeasurement. Pieces of information logged at different logging times arestored in different log entries.

The serving cell identity may include a cell identity in the layer 3,which is called a Global Cell Identity (GCI). The GCI is a set of aPhysical Cell Identity (PCI) and a PLMN identity.

Meanwhile, UE may perform logging by analyzing criteria related to theperformance of UE in addition to a radio environment. For example, thecriteria related to the performance of UE may include a throughput, anerroneous transmission/reception rate, etc.

Referring back to FIG. 14, the aforementioned logging phase and reportphase may be present in plural times for logging duration (S1441,S1442).

The eNB may record/store the logged measurement on/in a TCE when thelogged measurement is reported.

If the UE has logged measurement that has not been reported after thevalidity timer expires, that is, after the logging duration elapses, theUE performs a procedure for reporting the logged measurement to the eNB.A phase in which the overall procedure for the procedure is called apost-reporting phase.

When the logging duration expires, the UE discards the loggedmeasurement configuration and initiates a conservation timer. After thelogging duration is terminated, the UE suspends MDT measurement.However, the already logged measurement remains intact without beingdiscarded. The conservation timer indicates the lifetime of theremaining logged measurement.

When the UE enters the RRC_connected state (S1451) before theconservation timer expires, the UE may report logged measurement to theeNB. In this case, the aforementioned procedure for a logged measurementreport may be performed (S1452, S1453, S1454). When the conservationtimer expires, the remaining logged measurement may be discarded. Whenthe logged measurement is reported, the eNB may record/store the loggedmeasurement on/in the TCE.

The conservation timer may be fixed to a predetermined value in the UEand may be previously set in the UE. For example, a value of theconservation timer may be 48 hours. Or, a value of the conservationtimer may be included in the logged measurement configuration andtransferred to the UE or may be included in a different RRC message andtransferred to the UE.

Meanwhile, when a new logged measurement configuration is transferred tothe UE, the UE may update an existing logged measurement configurationinto the newly obtained logged measurement configuration. In this case,the validity timer can be started again from the time when the loggedmeasurement configuration is newly received. Furthermore, loggedmeasurement based on the previous logged measurement configuration maybe discarded.

FIG. 18 is a diagram showing an example of an immediate MDT. Theimmediate MDT is based on a Radio Resource Management (RRM) measurementand report mechanism. In addition, information related to the locationupon a measurement report is added and reported to an eNB.

Referring to FIG. 18, UE receives an RRC connection reconfigurationmessage (S1810) and transmits an RRC connection reconfiguration completemessage (S1820). Thus, the UE enters the RRC_connected state. The UE mayreceive a measurement configuration by receiving the RRC connectionreconfiguration message. In the example of FIG. 18, the measurementconfiguration has been illustrated as being received through the RRCconnection reconfiguration message, but the measurement configurationmay be included in a different RRC message and transmitted.

The UE performs measurement and evaluation in the RRC_connected state(S1831) and reports a measurement result to the eNB (S1832). In theimmediate MDT, the measurement result may provide precise locationinformation, as possible, as in the example of location informationprovided by a Global Navigation Satellite System (GNSS). For locationmeasurement, such as an RF fingerprint, the measurement result mayprovide measurement information about a neighboring cell, which may beused to determine the location of UE.

From FIG. 18, it may be seen that even after the executed measurementand evaluation (S1831) and the report (S1832), the UE reports ameasurement result (S1843) to the eNB right after performing measurementand evaluation (S1842). This is the biggest difference between thelogged MDT and the immediate MDT.

If one service provider manages a plurality of PLMNs, UE needs toperform measurement and/or a report on the plurality of PLMNs. This maybe an MDT or may be a report attributable to a radio link failure.

First, if a plurality of service providers has been agreed to use alogged MDT in common, UE needs to perform an operation for the MDT on aplurality of PLMNs.

However, the UE performs an MDT measurement and report only on an RPLMNwhen a measurement configuration for the MDT is received. It may not beeasy to configure an MDT in different UE in each PLMN with considerationtaken of that it is not easy to obtain a consent from the user of the UEregarding the execution of the MDT. Furthermore, there may be a problemin that the effectiveness of a logged MDT is deteriorated because thecontinuity of the logged MDT is not guaranteed at a point where the PLMNis changed, so-called a PLMN boundary.

Accordingly, there is a need for a mechanism in which a networkconfigures a plurality of PLMNs whose measurement configuration for anMDT is valid in UE and the UE continue to perform an MDT measurementoperation in the plurality of PLMNs.

In order to support the valid MDT for the plurality of PLMNs, there isproposed a method in which the network sets the logging of the UE andthe scope in which logged measurement will be reported. This method maybe embodied using a method in which the network configures a PLMN listin the UE or a method in which the network designates a specific celltype on which the MDT will be performed to the UE.

First, a method in which a network configures a PLMN list in UE isdescribed below. The UE receives information about a PLMN on which anMDT will be performed from a network. The UE determines a PLMN on whichthe UE will report measurement/logging and logged measurement, that is,a PLMN scope based on the received information about the PLMN. The UEperforms an MDT only when it is placed in a cell belonging to the PLMNscope.

As a method of configuring information about a PLMN and a method ofdetermining a PLMN scope, a method of including at least one PLMNidentity in information about a PLMN list may be proposed. This methodmay be proposed in the example of FIG. 19.

FIG. 19 is a flowchart illustrating an example of a method of performinga logged MDT based on a PLMN scope in accordance with an embodiment ofthe present invention. A PLMN A is assumed to be an RPLMN.

Referring to FIG. 19, UE receives a logged measurement configurationfrom a cell 1 (S1910). The logged measurement configuration includesinformation for the execution of the logged MDT and PLMN information.The PLMN information may be embodied in the form of a PLMN list. ThePLMN list includes identities of a PLMN B and a PLMN D.

The UE determines a PLMN scope based on the received PLMN information.In the present example, the UE includes all PLMNs, included in the PLMNlist, in the PLMN scope. Thereafter, the UE performs a logged MDT basedon the PLMN scope.

The UE performs MDT measurement based on the logged measurementconfiguration (S1920). Hereinafter, the execution of MDT measurement bythe UE may correspond to the aforementioned procedure of performing themeasurement of a logged MDT, logging a measurement result, and reportingthe logged measurement as in FIG. 14.

The UE performs MDT measurement and logs a measurement result in theRRC_idle state. When the UE enters the RRC_connected state, the UEreports the logged measurement to an eNB. To report the loggedmeasurement to the eNB may include that when the eNB is informed thatthe logged measurement is present and the eNB requests that the loggedmeasurement be reported, the logged measurement is reported in responseto the request. In order to inform the eNB that the logged measurementis present, the UE may include a logged measurement-available indicatorin an RRC connection configuration-confirm message, an RRC connectionreconfiguration-confirm message, or an RRC connectionreestablishment-confirm message, that is, a message through which the UEcompletes an RRC connection, and may transmit the RRC message.

The UE performs mobility to the cell 1 (S1931). Hereafter, the executionof mobility by the UE may be the execution of handover and/or cellselection/reselection.

The UE performs MDT measurement in the cell 1 (S1932). The UE mayperform the MDT measurement in the cell 1 because the cell 1 correspondsto the PLMN A, that is, an RPLMN of the UE, although the PLMN A is notincluded in the received PLMN list.

When the UE enters the RRC_connected state in the cell 1, if the UE haslogged measurement and the cell 1 is a cell corresponding to a PLMNincluded in the PLMN scope, the UE includes a loggedmeasurement-available indicator in an RRC message (an RRC connectionconfiguration-confirm message, an RRC connection reconfiguration-confirmmessage, or an RRC connection reestablishment-confirm message) andtransfer the RRC message to the eNB. Accordingly, the logged measurementcan be reported to the eNB. The UE enters the RRC_idle state and may loga measurement result because the cell 1 corresponds to a PLMN includedin the PLMN scope.

The UE performs mobility to the cell 2 (S1941) and performs MDTmeasurement in the cell 2 (S 1942). If the UE is in the RRC_connectedstate and has logged measurement, the UE may include a loggedmeasurement-available indicator in an RRC message and transmit the RRCmessage to the cell 2 because the cell 2 is a cell corresponding to thePLMN B included in the PLMN scope. Furthermore, if there is a requestfrom the cell 2, the UE may report the logged measurement. When the UEenters the RRC_idle state, the UE may log a measurement result becausethe cell 2 corresponds to a PLMN included in the PLMN scope.

The UE performs mobility to a cell 3 (S1951).

Meanwhile, since the cell 3 is a cell corresponding to the PLMN C andthe PLMN C is not included in the PLMN scope, the UE suspends the MDTmeasurement in the cell 3 (S1952).

Although the UE enters the RRC_connected state in the cell 3 and haslogged measurement, the UE may not report the logged measurement becausethe cell 3 is a cell corresponding to the PLMN C not included in thePLMN scope. That is, the UE may transmit a RRC connectionconfiguration-confirm message, an RRC connection reconfiguration-confirmmessage, or an RRC connection reestablishment-confirm message notincluding a logged measurement-available indicator.

Furthermore, although the UE enters the RRC_idle state in the cell 3,the UE may not log a measurement result because the cell 3 is a cellcorresponding to the PLMN C not included in the PLMN scope.

The UE performs mobility to the cell 2 (S1961) and performs MDTmeasurement in the cell 2 (S1962). For the MDT measurement, referencemay be made to step S1942 in which MDT measurement is performed in thecell 2.

FIG. 20 is a flowchart illustrating another example of a method ofperforming logged MDT measurement based on a PLMN scope in accordancewith an embodiment of the present invention.

In the present example, an Equivalent PLMN (EPLMN) is configured in UE.The EPLMN means a PLMN that the UE considers the PLMN to be equivalentto an RPLMN. When UE performs a procedure for being registered with anetwork, the UE may receive an EPLMN list from a network.

Referring to FIG. 20, UE receives a logged measurement configurationfrom a cell 1 (S2010). The logged measurement configuration includes theaforementioned information for MDT measurement and the PLMN information.The PLMN information may be embodied in the form of a PLMN list. ThePLMN list includes the identities of a PLMN B, a PLMN C, and a PLMN D.

The UE determines a PLMN scope based on the EPLMN list and the receivedPLMN information. In the present example, the UE may include only a PLMNincluded in the EPLMN list, from among all PLMNs included in the PLMNlist, in the PLMN scope. However, the PLMN A may be included in the PLMNscope irrespective of whether or not the PLMN A is included in the EPLMNlist and/or the received PLMN list because the PLMN A is an RPLMN. Inthe present example, the PLMN scope includes the PLMN B, the PLMN D, anda PLMN A.

The UE performs MDT measurement based on the logged measurementconfiguration (S2020). The UE performs the MDT measurement in theRRC_idle state and logs the performed MDT measurement. When the UEenters the RRC_connected state, the UE reports the logged measurement toan eNB. To report the logged measurement to the eNB may include that theeNB is informed that the logged measurement is present and that when theeNB requests that the logged measurement be reported, the loggedmeasurement is reported in response to the request. In order to informthe eNB that the logged measurement is present, the UE may include alogged measurement-available indicator in an RRC connectionconfiguration-confirm message, an RRC connection reconfiguration-confirmmessage, or an RRC connection reestablishment-confirm message, that is,a message through which the UE completes an RRC connection, and maytransmit the RRC message.

The UE performs mobility to the cell 1 (S2031) and performs MDTmeasurement in the cell 1 (S2032). The UE may perform the MDTmeasurement in the cell 1 because the cell 1 corresponds to the PLMN A,that is, an RPLMN of the UE, although the PLMN A is not included in thereceived PLMN list.

When the UE enters the RRC_connected state in the cell 1, if the UE haslogged measurement and the cell 1 is a cell corresponding to a PLMNincluded in the PLMN scope, the UE includes a loggedmeasurement-available indicator in an RRC message (an RRC connectionconfiguration-confirm message, an RRC connection reconfiguration-confirmmessage, or an RRC connection reestablishment-confirm message) andtransfer the RRC message to the eNB. Accordingly, the logged measurementcan be reported to the eNB. When the UE enters the RRC_idle state, theUE may log a measurement result because the cell 1 corresponds to a PLMNincluded in the PLMN scope.

The UE performs mobility to a cell 2 (S2041) and performs MDTmeasurement in the cell 2 (S2042). If the UE is in the RRC_connectedstate and has logged measurement, the UE may include a loggedmeasurement-available indicator in an RRC message and transmit the RRCmessage to the cell 2 because the cell 2 is a cell corresponding to thePLMN B included in the PLMN scope. Furthermore, if there is a requestfrom the cell 2, the UE may report the logged measurement. When the UEenters the RRC_idle state, the UE may log a measurement result becausethe cell 2 corresponds to a PLMN included in the PLMN scope.

The UE performs mobility to a cell 3 (S2051).

Meanwhile, the UE suspends the MDT measurement in the cell 3 because thecell 3 is a cell corresponding to the PLMN C and the PLMN C is notincluded in the PLMN scope (S2052).

Although the UE enters the RRC_connected state in the cell 3 and haslogged measurement, the UE may not report the logged measurement becausethe cell 3 is a cell corresponding to the PLMN C not included in thePLMN scope. That is, the UE may transmit a RRC connectionconfiguration-confirm message, an RRC connection reconfiguration-confirmmessage, or an RRC connection reestablishment-confirm message notincluding a logged measurement-available indicator.

Furthermore, although the UE enters the RRC_idle state in the cell 3,the UE may not log a measurement result because the cell 3 is a cellcorresponding to the PLMN C not included in the PLMN scope.

The UE performs mobility to the cell 2 (S2061) and performs MDTmeasurement in the cell 2 (S2062). For the execution of the MDTmeasurement in the cell 2, reference may be made to step S2042.

FIG. 21 is a flowchart illustrating yet another example of a method ofperforming logged MDT measurement based on a PLMN scope in accordancewith an embodiment of the present invention.

Information about a PLMN may be information indicating that which PLMNof an EPLMN list configured in UE is included in a PLMN scope. In thiscase, the information about a PLMN may be embodied in the form of a listof identities indicative of PLMNs included in the PLMN scope or may berepresented in a bitmap form. In the example of FIG. 21, the informationabout a PLMN indicates a method of indicating a PLMN included in a PLMNscope, from an EPLMN list, in a bitmap form.

The size of the bitmap is equal to the number of PLMNs within the EPLMNlist configured in UE. The bits of the bitmap are sequentiallyassociated with the respective PLMNs of the EPLMN list. A PLMN having 1associated with a bit of the bitmap may be included in the PLMN scope,and a PLMN having 0 associated with a bit of the bitmap may be excludedfrom the PLMN scope. Detailed bit values of the bitmap may be inverselyset.

Referring to FIG. 21, the UE receives an EPLMN list (S2111). The EPLMNlist for the UE may indicate PLMNs B, C, and D.

The UE receives a logged measurement configuration from a cell 1(S2112). The logged measurement configuration includes theaforementioned information for MDT measurement and the PLMN information.The PLMN information may include a PLMN indication bitmap indicative ofa PLMN to be included in a PLMN scope. In the present example, a valueof the bitmap may be set to (1 0 1).

The UE determines a PLMN scope based on the EPLMN list and the receivedPLMN information. If a value indicating that a bit of the bitmap,corresponding to a PLMN included in the EPLMN list, is included is ‘1’,for example, the UE determines that the corresponding PLMN is includedin the PLMN scope. In contrast, if a value indicating that a bit of thebitmap, corresponding to a PLMN included in the EPLMN list, is notincluded is ‘0’, for example, the UE may exclude the corresponding PLMNfrom the PLMN scope. However, the PLMN A may be included in the PLMNscope irrespective of whether or not the PLMN A is included in the EPLMNlist and/or the received PLMN list because the PLMN A is an RPLMN. Inthe present example, the PLMN scope includes the PLMN B, the PLMN D, anda PLMN A.

The UE performs MDT measurement based on the logged measurementconfiguration (S2120). The UE performs MDT measurement in the RRC_idlestate and logs the MDT measurement. When the UE enters the RRC_connectedstate, the UE reports the logged measurement to the eNB. To report thelogged measurement to the eNB may include that the eNB is informed thatthe logged measurement is present and that when the eNB requests thatthe logged measurement be reported, the logged measurement is reportedin response to the request. In order to inform the eNB that the loggedmeasurement is present, the UE may include a loggedmeasurement-available indicator in an RRC connectionconfiguration-confirm message, an RRC connection reconfiguration-confirmmessage, or an RRC connection reestablishment-confirm message, that is,a message through which the UE completes an RRC connection, and maytransmit the RRC message.

The UE performs mobility to the cell 1 (S2131) and performs MDTmeasurement in the cell 1 (S2132). The UE may perform the MDTmeasurement in the cell 1 because the cell 1 corresponds to the PLMN A,that is, an RPLMN of the UE, although the PLMN A is not included in thereceived PLMN list.

When the UE enters the RRC_connected state in the cell 1, if the UE haslogged measurement and the cell 1 is a cell corresponding to a PLMNincluded in the PLMN scope, the UE may include a loggedmeasurement-available indicator in an RRC message (an RRC connectionconfiguration-confirm message, an RRC connection reconfiguration-confirmmessage, or an RRC connection reestablishment-confirm message) andtransfer the RRC message to the eNB. Accordingly, the UE can report thelogged measurement to the eNB. The UE enters the RRC_idle state and maylog a measurement result because the cell 1 corresponds to a PLMNincluded in the PLMN scope.

The UE performs mobility to a cell 2 (S2141) and performs MDTmeasurement in the cell 2 (S2142). If the UE is in the RRC_connectedstate and has logged measurement, the UE may include a loggedmeasurement-available indicator in an RRC message and transmit the RRCmessage to the cell 2 because the cell 2 is a cell corresponding to thePLMN B included in the PLMN scope. Furthermore, if there is a requestfrom the cell 2, the UE may report the logged measurement. When the UEenters the RRC_idle state, the UE may log a measurement result becausethe cell 2 corresponds to a PLMN included in the PLMN scope.

The UE performs mobility to a cell 3 (S2151).

Meanwhile, since the cell 3 is a cell corresponding to the PLMN C andthe PLMN C is not included in the PLMN scope, the UE suspends the MDTmeasurement in the cell 3 (S2152).

Although the UE enters the RRC_connected state in the cell 3 and haslogged measurement, the UE may not report the logged measurement becausethe cell 3 is a cell corresponding to the PLMN C not included in thePLMN scope. That is, the UE may transmit a RRC connectionconfiguration-confirm message, an RRC connection reconfiguration-confirmmessage, or an RRC connection reestablishment-confirm message notincluding a logged measurement-available indicator.

Furthermore, although the UE enters the RRC_idle state in the cell 3,the UE may not log a measurement result because the cell 3 is a cellcorresponding to the PLMN C not included in the PLMN scope.

The UE performs mobility to the cell 2 (S2161) and performs MDTmeasurement in the cell 2 (S2162). For the MDT measurement performed inthe cell 2, reference may be made to step S2142.

In the MDT performed based on the PLMN scope described with reference toFIGS. 19 to 21, the RPLMN has been assumed to be included in the PLMNscope. However, an embodiment in which an RPLMN is not included in aPLMN scope may also be embodied. In this case, in FIGS. 19 to 21, the UEmay suspend MDT measurement in the cell 1 corresponding to the PLMN A,as in the operation of the UE in the cell 3. The network may provide theUE with additional signaling indicating whether or not an RPLMN will beincluded in the PLMN scope.

In the examples of FIGS. 19 to 21, the PLMN information has beenillustrated as being included in the logged measurement configurationand transmitted, but the transmission of the PLMN information is notlimited thereto. The PLMN information may be transferred to the UEthrough additional RRC signaling or may be transferred to the UE throughNAS signaling.

Whether or not a PLMN is present in a PLMN scope may be embodied bycomparing the identity list of the PLMN scope with the PLMN identity ofa target cell. UE may determine that the PLMN of a corresponding cell isincluded in the PLMN scope if the PLMN identity of the target cell isincluded in the identity list of the PLMN scope and may determine thatthat the PLMN of the corresponding cell is not included in the PLMNscope if the PLMN identity of the target cell is not included in theidentity list of the PLMN scope.

The MDT of FIGS. 19 to 21 shows an example of a method of performing alogged MDT, but the use of PLMN information may also be applied to animmediate MDT. The immediate MDT is different from a logged MDT in thata detailed operation of UE for performing MDT measurement and reportincludes excluding logging and reporting a measurement result rightafter the measurement. However, a basic mechanism for determining a PLMNscope based on PLMN information, determining whether or not to performmeasurement and a report based on a result of the determination, andperforming MDT measurement may be clearly induced from the embodimentsof FIGS. 19 to 21.

A network may provide an MDT measurement method for reporting loggedmeasurement in relation to a cell corresponding to a specific cell type.

UE obtains the type of cell on which an MDT will be performed from anetwork. Here, a cell type indicative of a CSG cell may be received asthe type of specific cell. In this case, the UE performs an MDT onlywhen the UE is placed in the CSG cell.

A cell type indicative of an MBMS cell may be received as the type ofspecific cell. In this case, UE may perform an MDT only when a servingcell is the MBMS cell. The MBMS cell refers to a cell that provides MBMSservice.

In contrast, indication information instructing that an MDT should notto be performed on a specific cell type may be provided to UE. In thiscase, the UE may perform an MDT only when a cell not corresponding tothe specific cell type is a serving cell. For example, when UE receivesindication information instructing that an MDT should not to beperformed on a CSG cell, the UE may perform an MDT only when the UE isplaced in a cell not corresponding to the CSG cell.

Meanwhile, to report a result based on the aforementioned PLMN scope mayalso be applied to a radio link failure report and a handover failurereport.

The radio link failure described with reference to FIG. 7 may begenerated in response to the generation of a PHY layer problem in theRRC_connected state, the generation of a random access problem, or aretransmission-related indication on the RLC side.

When a radio link failure or handover failure is detected, UE generatesradio link failure report information. Information about the radio linkfailure may include information about a PLMN identity corresponding to acell having a radio link failure, the recent measurement result of aserving cell (may include RSRP and RSRQ), a measurement result of aneighboring cell, information about the location of UE, and a globalcell identity of a cell having a radio link failure. If UE generatesradio link failure information attributable to a radio link failure, theUE may include information indicating that the corresponding informationhas been generated due to the radio link failure. If UE generates radiolink failure information attributable to a handover failure, the UE mayinclude information indicating that the corresponding information hasbeen generated due to the handover failure.

Thereafter, if UE has configured an RRC connection with a specific cell,the UE may send information about a radio link failure to acorresponding cell. Here, if the PLMN of the specific cell correspondsto an RPLMN of the UE or the PLMN of the specific cell is included in aPLMN scope, the UE may send the information about the radio linkfailure.

If a radio link fails, UE may report the radio link failure to anetwork. To report the radio link failure by the UE may be initiated bysending a message through which the UE completes an RRC connection withthe network. In order to inform that the radio link failure to bereported is present, the UE may include a radio link failure availableindicator in an RRC connection complete message (an RRC connectionconfiguration-confirm message, an RRC connection reconfiguration-confirmmessage, or an RRC connection reestablishment-confirm message) and sendthe RRC connection complete message.

An eNB of a cell checks a radio link failure available indicator. If theeNB checks that radio link failure information to be reported by UE ispresent, the eNB transmits a message, requesting to obtain UEinformation, to the UE. In response thereto, the UE transmits a UEinformation response message, including the radio link failureinformation, to the eNB.

If an RRC connection with a cell corresponding to a PLMN not included ina PLMN scope has been established, UE may not report radio link failureinformation.

An example of a method of reporting a radio link failure based on a PLMNscope is described with reference to FIG. 22.

FIG. 22 is a diagram showing an example of a method of reporting a radiolink failure based on a PLMN scope.

Referring to FIG. 22, UE receives PLMN information from a specific celland determines a PLMN scope (S2210). The embodiment of the PLMNinformation and the determination of the PLMN scope based on the PLMNinformation may be performed in a similar manner to that described withreference to FIGS. 19 to 21. In the present example, a PLMN B and a PLMND are assumed to be included in the PLMN scope. The PLMN information maybe included in a logged measurement configuration and transmitted or maybe included in a different RRC message and transmitted. Although notshown, the PLMN scope may include or may not include a PLMN A, that is,an RPLMN.

The UE generates information about a radio link failure when the radiolink failure is detected (S2220).

Thereafter, the UE performs mobility to a cell 3 and establishes an RRCconnection (S2230). To perform mobility to the cell 3 by the UE mayinclude that cell selection, cell reselection and/or handover isperformed using the cell 3 as a target cell. The UE may not sendinformation about the radio link failure because the PLMN of the cell 3is a PLMN C and is not included in the PLMN scope. Accordingly, the UEdoes not include a radio link failure available indicator in an RRCconnection-confirm message (an RRC connection configuration-confirmmessage, an RRC connection reconfiguration-confirm message, or an RRCconnection reestablishment-confirm message) that is transmitted when anRRC connection is set up.

Thereafter, the UE detects a radio link failure again (S2240). In thiscase, the UE may initialize already generated information about theradio link failure. The UE generates new information about the radiolink failure.

Thereafter, the UE performs mobility to a cell 2 and establishes an RRCconnection (S2250). The UE may determine that the PLMN of the cell 2 isthe PLMN B and includes in the PLMN scope. Accordingly, the UE includesa radio link failure available indicator in an RRC connection-confirmmessage (an RRC connection configuration-confirm message, an RRCconnection reconfiguration-confirm message, or an RRC connectionreestablishment-confirm message) that is transmitted when an RRCconnection is set up. The eNB of the cell 2 transmits a message thatrequests information about the radio link failure, and the UE maytransmit a UE information response message, including information aboutthe radio link failure, to the eNB.

As described above, in a wireless communication system in which aplurality of PLMNs is present, UE may selectively transmit informationabout a radio link failure in relation to a cell corresponding to aspecific PLMN based on a PLMN scope.

If an MDT is performed based on a PLMN scope or information about aradio link failure is transmitted to a network as described above, aservice provider may obtain information about logged measurement or aradio link failure of UE over a plurality of PLMNs. A service providermay optimize a network more efficiently based on the obtainedinformation.

FIG. 23 is a block diagram showing a radio apparatus in which anembodiment of the present invention may be embodied. The apparatus maybe embodied in the operation of UE in the embodiments of FIGS. 19 to 22.

The radio apparatus 2300 includes a processor 2310, memory 2320, and aRadio Frequency (RF) unit 2330. The processor 2310 embodies the proposedfunctions, processes and/or methods. The processor 2310 may receive PLMNinformation and determine a PLMN scope. The processor 2310 may check anRRC state and perform an MDT based on a result of the check. Theprocessor 2310 may perform measurement and immediately report themeasurement or may log a measurement result and report the loggedmeasurement result. The processor 2310 may perform the MDT based on thePLMN scope. The processor 2310 may detect a radio link failure and/or ahandover failure and generate information about the radio link failure.The processor 2310 may report the information about the radio linkfailure based on the PLMN scope. The embodiments of FIGS. 19 to 22 maybe embodied by the processor 2310 and the memory 2320.

The RF unit 2330 is connected to the processor 2310 and transmits andreceives radio signals.

The processor may include Application-Specific Integrated Circuits(ASICs), other chipsets, logic circuits, and/or data processors. Thememory may include Read-Only Memory (ROM), Random Access Memory (RAM),flash memory, memory cards, storage media and/or other storage devices.The RF unit may include a baseband circuit for processing radio signals.When the above-described embodiment is implemented in software, theabove-described scheme may be implemented into a module (process orfunction) configured to perform the above function. The module may bestored in the memory and executed by the processor. The memory may beplaced inside or outside the processor and connected to the processorusing a variety of well-known means.

In the above exemplary system, although the methods have been describedbased on the flowcharts in the form of a series of steps or blocks, thepresent invention is not limited to the sequence of the steps, and someof the steps may be performed in a different order from that of othersteps or may be performed simultaneous to other steps. Furthermore,those skilled in the art will understand that the steps shown in theflowchart are not exclusive and the steps may include additional stepsor that one or more steps in the flowchart may be deleted withoutaffecting the scope of the present invention.

1. A method for reporting performed by user equipment (UE) in a wirelesscommunication system, comprising: receiving a Public Land Mobile Network(PLMN) list that is information about at least one PLMN whose loggedMinimization Drive Test (MDT) is valid; receiving information forexecuting the logged MDT; logging measurement based on the informationfor executing the logged MDT; entering a Radio Resource Control(RRC)_connected state for a target cell; determining whether reportingthe logged measurement is possible or not; and reporting part of or fulllogged measurement to the target cell if reporting the loggedmeasurement to the target cell is possible, wherein determining whetherreporting the logged measurement is possible or not is based on the PLMNlist.
 2. The method of claim 1, wherein the PLMN list comprises at leastone identity of the at least one PLMN.
 3. The method of claim 2, whereindetermining whether reporting the logged measurement is possible or notcomprises, determining that reporting the logged measurement to thetarget cell is possible, if an identity of a PLMN for the target cell isincluded in the at least one identity of the at least one PLMN in thePLMN list and the logged measurement to be reported to the target cellis present.
 4. The method of claim 3, wherein the PLMN list and theinformation for performing the logged MDT are transmitted in a loggedmeasurement configuration that is an RRC message.
 5. The method of claim1, wherein reporting the part of or the full logged measurement to thetarget cell comprises: sending a logged measurement-available indicatorto the target cell, the logged measurement-available indicatorindicating that the logged measurement to be reported to the target cellis present; receiving a measurement report request from the target cellas a response to the logged measurement-available indicator; and sendingthe part of or the full logged measurement to the target cell inresponse to the measurement report request.
 6. The method of claim 1,wherein the information for the logged MDT measurement comprises:logging duration indicating duration for which the logged MDT isperformed; and a logging interval indicating an interval in which thelogging is performed.
 7. The method of claim 6, wherein logging themeasurement comprises: logging measurement every interval within thelogging duration from a point of time at which the information for thelogged MDT measurement is received; and suspending the logging when theduration elapses.
 8. A wireless apparatus comprising: a transceivertransmitting and receiving radio signals; and a processor is operablycoupled to the transceiver, the processor is configured to: receiveinformation for executing the logged Minimization Driving Test (MDT);log measurement based on the information for executing the logged MDT;enter a Radio Resource Control (RRC)_connected state for a target cell;determine whether reporting the logged measurement is possible or not;and report part of or full logged measurement to the target cell ifreporting the logged measurement to the target cell is possible, whereindetermining whether reporting the logged measurement is possible or notis based on the PLMN list.
 9. The wireless apparatus of claim 8, whereinthe PLMN list comprises at least one identity of the at least one PLMN.10. The wireless apparatus of claim 9, wherein determining whetherreporting the logged measurement is possible or not comprisesdetermining that reporting the logged measurement to the target cell ispossible, if an identity of a PLMN for the target cell is included inthe at least one identity of the at least one PLMN in the PLMN list andthe logged measurement to be reported to the target cell is present. 11.The wireless apparatus of claim 10, wherein the PLMN list and theinformation for performing the logged MDT are transmitted in a loggedmeasurement configuration that is an RRC message.
 12. A method forreporting performed by a user equipment (UE) in a wireless communicationsystem, comprising: receiving a Public Land Mobile Network (PLMN) listthat is information about a PLMN whose radio link failure report isvalid; detecting a radio link failure; generating radio link failureinformation that is information about the radio link failure; entering aRadio Resource Control (RRC)_connected state for a target cell;determining whether reporting the radio link failure information to thetarget cell is possible or not; and reporting the radio link failureinformation to the target cell if reporting the radio link failureinformation to the target cell is possible, wherein determining whetherreporting the radio link failure information to the target cell ispossible or not is based on the PLMN list.
 13. The report method ofclaim 12, wherein the PLMN list comprises at least one identity of theat least one PLMN.
 14. The report method of claim 13, whereindetermining whether reporting the radio link failure information ispossible or not comprises determining that reporting the radio linkfailure information to the target cell is possible if an identity of aPLMN for the target cell is included in the at least one identity of theat least one PLMN in the PLMN list and the radio link failureinformation to be reported to the target cell is present.